TANTALUM AND TITANIUM ALKYLIDENE COMPLEXES BEARING PHOSPHINOALKOXIDE LIGANDS - REVERSIBLE ORTHO-METALATION OF A TITANIUM ALKYLIDENE

We have prepared dineopentyltantalum and -titanium complexes with phosphinoalkoxide ligands. It appears that the corresponding alkylidene complexes are readily formed by expulsion of neopentane. The molecular structure of one of the tantalum complexes was determined by X-ray crystal structure analysis. Crystal data: [TaCl2(CHMe(3))({OCMe(CH2-PPh(2))(2)}] space group = P2(1)/n (No. 14), a = 9.021(3) Angstrom, b = 20.333(6) Angstrom, c = 17.892(5) Angstrom, beta = 102.95(2)degrees, Z = 4, N-0, 4981, R = 0.045. The titanium alkylidene complexes react with the ligand backbone by addition of a phenyl CH fragment across the titanium-carbon double bond leading to a complex with a metalated phenyl moiety and a neopentyl group. Interestingly, the addition reaction is reversible. The structure of metalation product, was determined by X-ray crystal structure analysis and NMR spectroscopy. Crystal data: [Ti eta(5)-C5H5)(CH(2)CMe(3))(OC(t)BuCH(2)PPh-0C6H4) space group = C2 (No. 5), a = 28.759(9) Angstrom, b =8.767(2) Angstrom, c 11.722(3) Angstrom, beta P = 98.67(3)degrees, Z = 4, R = 0.037.